Hereafter, a wireless transmit/receive unit (WTRU) includes, but is not limited to, a user equipment, mobile station fixed or mobile subscriber unit, pager, or any other type of device capable of operating in a wireless environment. When referred to hereafter, a base station includes, but is not limited to, a base station, Node B, site controller, access point or other interfacing device in a wireless environment.
FIG. 3 shows a block diagram of an exemplary wireless system, in this case according to the third generation partnership program (3GPP) wideband code division multiple access (W-CDMA) protocol. Communication system 10 comprises RNC 11, base station 14 and WTRU 16. RNC 11 and base station are part of a universal mobile telecommunications system (UMTS) terrestrial radio access network (UTRAN)). RNC 11 controls the radio resources of system 10 interfaces (e.g., frequencies, scrambling codes, spreading factors, and channel power), and comprises radio resource control (RRC) entity 12, medium access control (MAC) entity 13, and frame protocol (FP) entity 25. Logical channels 22 are defined between RRC 12 and MAC 13 for signaling data transfer services. Transport channels are defined on line 24 between MAC 13 and FP 25. MAC control line 23 is used for transfer of control information between MAC 13 and RRC 12.
Base station 14 is responsible for radio transmission and reception in one or more cells with WTRU 16. Interface 21 is an interconnection between the radio network at RNC 11 and base station 14. Base station 14 transmits on downlink (DL) signals 15 to WTRU 16. Uplink (UL) signals 26 are transmitted from WTRU 16 to base station 14.
A variety of services, such as video, voice and data, each having different Quality of Service (QoS) requirements, can be transmitted using a single wireless connection. This is accomplished by multiplexing several transport channels (TrCHs), each service on its own TrCH, onto a coded composite transport channel (CCTrCh). The transmitted information is sent in units of transport blocks (TBs). The rate at which each service is transmitted is on a transmission time interval (TTI). The smallest interval is one frame of data, typically defined as 10 ms for a 3GPP communication system. Depending on the service type parameters, several TBs may transmit in a single TTI.
In wireless communications, one of the most important features in maintaining the communication link quality under fading and interference situations is power control. A critical parameter that is monitored for effective power control is signal to interference ratio (SIR). Transmission power is controlled by comparing a received SIR to a target SIR and adjusting the transmit power up or down accordingly.
In 3GPP-like communication system such as system 10, in either time division duplex (TDD) mode or frequency division duplex (FDD) mode, RRC 12 sets the initial target SIR of WTRU 16 at the call session establishment and then subsequently continuously adjusts the target SIR of WTRU 16 during the life term of the call. The target SIR is sent to WTRU 16 by RRC 12. Power control is divided by initialization and steady state phases, each with separate BLER reporting requirements. The initialization phase of power control is for quickly establishing a target SIR value. The steady state phase of power control is more refined, and starts efficiently with the benefit of the SIR target established during the initialization phase.
The QoS requirement of each transmitted service can be monitored at the transport block level in terms of a block error rate (BLER). Consequently, each TrCH has its own target BLER, against which the measured or estimated BLER is regularly compared to ensure acceptable service quality. In order to monitor the BLER level on a CCTrCH basis, a reference transport channel (RTrCH) may be selected among the transport channels multiplexed on the considered CCTrCH.
An inner loop power control algorithm sets the power of the UL signal 26. The transmit power adjustment of WTRU 16 is based on receipt of the target SIR generated from outer loop power control performed in RNC 11. WTRU 16 receives the target SIR adjustment signal and estimates of downlink channels and responds by setting its output power to a specific value.
An outer loop power control algorithm performed by RNC 11 operates using BLER estimation to control the target SIR for the inner loop power control. The UL outer loop power control controls the target SIR to maintain the received BLER as close as possible to a target BLER based on the cyclic redundancy code (CRC) of the data. Upon receipt of the UL 26 signal, MAC 13 performs an estimation of the BLER and sends a BLER estimate report to RRC 12 across MAC control path 23. RRC 12 then performs target SIR adjustment if necessary. The output from the UL outer loop power control is a new target SIR per CCTrCH sent along with DL 15 for each UL inner loop power control.